Turntable welding system with light curtain protection

ABSTRACT

A robotic welding system is provided that includes multiple welding cells equidistantly spaced in a circular arrangement, multiple perimeter light curtains to provide safety protection around the welding cells, a turntable centrally located in the circular arrangement, and multiple welding robots attached to the turntable. The welding system further includes a first welding process and a second welding process whereby both the first welding process and the second welding process each include a primary welding operation and a secondary welding operation whereby the turntable rotates between the welding cells to perform the primary and secondary welding operations.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a welding machine and morespecifically, to a multi-cell robotic welding system wherein at leastone welding robot is rotated, via a turntable, to each cell to perform awelding operation.

2. Description of Related Art

In a conventional robotic welding system typically a fixture containingcomponents to be welded into a welded assembly are transported to awelding area so a welding robot or robots can perform a welding process.The welded assembly must be removed from the welding area so asubsequent fixture with components for a subsequent welded assembly canundergo the welding process. A disadvantage of this process is that thewelding robot(s) is idle during the removal of the first fixture fromthe welding area and the placement of the subsequent fixture into thewelding area. This in turn increases production time and costs.

Further, conventional robotic welding systems take up substantial floorspace due to the arrangement of the welding robot with respect to thewelding cells or stations. This leads to increased manufacturing costsdue the substantial floor space required by the system.

Thus, what is required is a robotic welding system to overcome the abovementioned disadvantages.

SUMMARY OF THE INVENTION

In accordance with one aspect, the present invention overcomes the abovementioned disadvantages by providing a robotic welding system thatincludes multiple welding cells equidistantly spaced in a circulararrangement, multiple perimeter light curtains positioned at a perimeterof the multiple welding cells, a turntable centrally located in thecircular arrangement, the turntable having a rotating portion and astationary portion, and multiple welding robots operatively attached tothe rotating portion of the turntable. A first welding process isperformed in a first pair of the multiple welding cells and a secondwelding process is performed in a second pair of the multiple weldingcells, whereby the first welding process may be substantially differentfrom the second welding process. During the first welding process thewelding robots rotate between the first pair of welding cells while thesecond pair of welding cells are prepared for the second weldingprocess. Further, during the second welding process the welding robotsrotate between the second pair of welding cells while the first pair ofwelding cells are prepared for the first welding process.

In accordance with another aspect, the present invention furtherprovides where both the first pair and the second pair of welding cellseach include a primary welding cell and a secondary welding cell.Further, the first welding process and the second welding process eachinclude a primary welding operation performed in the primary weldingcell and a secondary welding operation performed in the secondarywelding cell. Still further, the primary welding operation issubstantially different from the secondary welding operation.

In accordance with yet another aspect, the present invention furtherprovides a method to permit humans and a rotatable robot access to workareas. Specifically, the present invention includes an arrangement oflight curtains that automatically activate and deactivate depending on aposition of the robot. When activated, the light curtains create asafety curtain that detects entry into the work area. When the safetycurtain is broken or disrupted, such as when a human enters the workarea, power is removed from the robot thereby preventing injury to thehuman.

Additional benefits and advantages of the present invention will becomeapparent to those skilled in the art to which it pertains upon a readingand understanding of the following detailed specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangement ofparts, a preferred embodiment of which will be described in detail inthis specification and illustrated in the accompanying drawings thatform a part of the specification.

FIG. 1 shows an overview of a turntable welding system in anon-operational state.

FIG. 2 shows an overview of the turntable welding system in anoperational state.

FIG. 3 is a side view of a turntable.

FIG. 4 is a schematic view of proximity switches.

FIG. 5 is a chart showing the activation and deactivation of lightcurtains in conjunction with the position of the turntable.

FIG. 6 is a chart showing the operation of proximity switches inconjunction with the position of the turntable.

FIG. 7 is a flowchart showing the operation of the turntable weldingsystem.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIG. 1 shows a schematic overview of aturntable welding system 10 that includes, multiple welding cells orstations 12-1, 12-2, 12-3, 12-4 (hereinafter collectively referred to as“welding cells 12-X”), multiple safety-light curtains 14, a turntable16, and multiple welding robots 18.

The multiple welding cells 12-X are equidistantly spaced in a circulararrangement. In the embodiment shown in the figures there is a first12-1, a second 12-2, a third 12-3, and a fourth 12-4 welding cell, thus,the welding cells 12-X are spaced in 90° intervals. It should be noted,however, that the present invention is not dependent on the number ofwelding cells. The number of welding cells may vary depending on theapplication. Thus, the embodiment shown in the figures is forillustrative purposes only and is not intended to limit the scope of thepresent invention. The welding cells 12-X contain equipment commonlyknown in the art, such as, a lift hoist to lift and move heavy objects,safety bars, safety switches, etc. and will not be described in detailherein. Thus, only those features that pertain to the present inventionwill be described.

The four welding cells 12-X are divided into two pairs such that a firstwelding process P1 is performed over a first time period in the firstpair of welding cells 12-X and a second welding process P2 is performedover a second time period in the second pair of welding cells 12-Xwhereby the first time period occurs at a different time period than thesecond time period. Specifically, the first welding process P1 isperformed in the first 12-1 and second 12-2 welding cells during thefirst time period, and the second welding process P2 is performed in thethird 12-3 and the fourth 12-4 welding cells during the second timeperiod. Of course, the second welding process P2 can be performed in thefirst 12-1 and second 12-2 welding cells, and the first welding processP1 can be performed in the third and fourth welding cells. Each weldingprocess P1, P2 is programmed into a control system to perform aparticular welding process for a specific application whereby the firstwelding process P1 may be different than the second welding process P2.

Each welding process P1, P2 is divided into two separate weldingoperations. Specifically, the first welding process P1 has a primarywelding operation P1-P that is performed in the first (or primary)welding cell 12-1, and a secondary welding operation P1-S that isperformed in the second (or secondary) welding cell 12-2, whereby theprimary welding operation P1-P is different than the secondary weldingoperation P1-S. Similarly, the second welding process P2 has a primarywelding process P2-P that is performed in the third (or primary) weldingcell 12-3 and a secondary welding process P2-S that is performed in thefourth (or secondary) welding cell 12-4, whereby the primary weldingoperation P2-P is different than the secondary welding operation P2-S.

Each welding cell 12-X includes a welding area 20 and two personnel workareas 22 located on either side of the welding area 20. The welding area20 is the portion of the welding cell 12-X where welding robot performsa welding operation. The work areas 22 are the portion of the weldingcell 12-X where personnel can enter the welding cell 12-X to make theappropriate changes to the welding area 20 when the welding cell 12-X isdeactivated. Any reference to a front portion of either the welding area20 or the work area 22 will be that portion closest to the turntable 16and any reference to a rear portion of the welding area 20 or work area22 will be that portion furthest from the turntable 16.

Still referring to FIG. 1, a pivoting gate 24 is located at the rearportion of each welding area 20 to allow personnel access to the weldingarea 20 to change out a fixture or a jig, as will be described furtherbelow. The gate 24 is electrically connected to a lockable E-stoppushbutton 26. The lockable E-stop pushbutton 26 serves two functions.First, the lockable E-stop pushbutton 26 serves as an emergency stoppushbutton that when activated prevents the robots 18 from operating inthat specific welding cell 12-x. The robots 18, however, will operate inthe other welding cells 12-x. Second the lockable E-stop pushbutton 26serves as a lockout so that when the gate 24 is open the lockable E-stoppushbutton 26 can be locked out so that the welding robots 18 cannotenter that specific welding cell 12-x. The welding robots 18, however,can enter the remaining welding cells 12-x. In other words, eachlockable E-stop pushbutton 26 operates only in conjunction with it'scorresponding welding cell 12-X. For example, if the gate 24 for thefirst welding cell 12-1 is open, the welding robots 18 can still operatein any remaining welding cell 12-2, 12-3, 12-4.

The welding cells 12-x are guarded by the light curtains 14 to safeguardthe personnel workers from accidental injury. Briefly, light curtainsare safety devices that are used to guard a manufacturing machine orarea by detecting inadvertent entry into the area. Light curtains use anarray of photoelectric sensors to detect the presence of an object, andtypically consist of an infrared transmitter post and a correspondinginfrared receiver post. When activated photoelectric transmitters fromthe first post project an array of synchronized-parallel infrared lightbeams to the receivers in the second post, thereby forming a safetycurtain plane or detection zone. When an object interrupts one or morelight beams a corresponding electrical safety circuit removes power fromthe guarded area to ensure safety. In the present invention, the lightcurtains 14 detect entry into the welding cells 12-X. Specifically, thelight curtains 14 detect inadvertent entry into the activated weldingcell 12-X.

Each welding cell 12-X includes multiple light curtains 14.Specifically, each welding cell 12-X includes a pair of perimetervertical light curtains 14-V, a pair of perimeter horizontal lightcurtains 14-H, and an inner light curtain 14-I. It should be noted thatthe light curtains for a specific welding cell 12-X will be referencedhereinafter in the specification and on the drawings by simply addingthe welding cell number to the end of the light curtain referencenumber. For example, the perimeter vertical light curtains for the firstwelding cell 12-1 will be referenced as 14-V1, the perimeter horizontallight curtains for welding cell 12-1 will be referenced as 14-H1, theinner light curtains for welding cell 12-1 will be referenced as 14-I1,etc. It should be further noted that because all the light curtains14-V, 14-H, 14-I are identical for each welding cell 12-X only the lightcurtains in reference to the first welding cell 12-1 will be describedand shown in the figures.

Referring to FIG. 2 and to the first welding cell 12-1, each perimetervertical light curtain 14-V1 has a vertical transmitter post and avertical receiving post. The perimeter vertical light curtains 14-V1create a vertical safety curtain 34 that is activated (shown as a solidline) when the welding robots 18 are performing a welding operation inthe first welding cell 12-1. Each perimeter vertical light curtain 14-V1further includes a corner mirror 14-M1. The corner mirror 14-M1 allowsthe infrared beam to be bent around a 90° corner from the transmitterpost to the receiving post. The presence of the corner mirror 14-M1allows multi-side protection without increasing the number of lightcurtains. Thus, as shown in FIG. 2, when activated the perimetervertical light curtains 14-V1 detect entry into the welding cell 12-1from the back portion of each work area 22 and from the side of eachwork area 22. It should be noted that when one set of perimeter verticallight curtains 14-V is activated for a given welding cell 12-X the otherthree sets of perimeter vertical light curtains 14-V are deactivated (asshown with dashed lines). Thus, in the embodiment shown in the figures,perimeter vertical light curtain 14-V1 for the first welding cell 12-1is activated and perimeter vertical light curtains 14-V2, 14-V3, and14-V4 for the second welding cell 12-2, the third welding cell 12-3, andthe fourth welding cell 14-4 respectively are deactivated.

Still referring to FIG. 2 and to the first welding cell 12-1, eachperimeter horizontal light curtain 14-H1 has a horizontal transmitterpost located at the rear portion of the work area 22 and a horizontalreceiver post located at the front portion of the work area 22. Theperimeter horizontal light curtain 14-H1 creates a horizontal safetyplane 40 that is located approximately 1-3 feet above the surface of thework area 22. The horizontal safety plane 40 is activated (shown ascross-section lines) when the welding robots 18 are performing a weldingoperation in the first welding cell 12-1. If the perimeter horizontallight curtain 14-H1 is activated while a personnel worker is in the workarea 22 the welding robots 18 cannot start the welding operation in thefirst welding cell 12-1 because, as explained above, interruption of thelight beam removes power from the guarded area. It should be noted thatwhen one set of perimeter horizontal light curtains 14-H is activatedfor a given welding cell 12-X the other three sets of perimeterhorizontal light curtains 14-H are deactivated (no cross-section linesshown). Thus, in the embodiment shown in the figures, perimeterhorizontal light curtain 14-H1 for the first welding cell 12-1 isactivated and perimeter horizontal light curtains 14-H2, 14-H3, and14-H4 for the second welding cell 12-2, the third welding cell 12-3, andthe fourth welding cell 14-4 respectively are deactivated.

Still referring to FIG. 2 and to the first welding cell 12-1, the innerlight curtain 14-I1 is located adjacent to the turntable 16 and extendsalong the front portion of the welding area 20 and the two work areas22. The inner light curtain 14-I1 also includes a vertical transmitterpost and a vertical receiving post that creates a vertical safetycurtain to detect access into the turntable area. The inner lightcurtain 14-I1, however, is deactivated (shown with dashed lines) whenthe perimeter vertical light curtains 14-V1 and the perimeter horizontallight curtains 14-H1 are activated. As shown in FIG. 2, the weldingrobots 18 extend between the vertical transmitter post and the verticalreceiving post of the inner light curtain 14-I1. Thus, in order for thewelding robots 18 to access the welding area 20 of the first weldingcell 12-1 the inner light curtain 14-I1 must be deactivated. It shouldbe noted that when one of the inner light curtains 14-I is deactivatedfor a given welding cell 12-X the other three inner light curtains 14-Iare activated (shown with solid lines). Thus, in the embodiment shown inthe figures, the inner light curtain 14-I1 for the first welding cell12-1 is deactivated and the inner light curtains 14-I2, 14-I3, and 14-I4for the second welding cell 12-2, the third welding cell 12-3, and thefourth welding cell 14-4 respectively are activated.

Referring to FIGS. 2 and 3, the turntable 16 is motor driven and ispositioned at a center of the circular arrangement of the welding cells12-X. The turntable 16 is of the type commonly known in the art and onlythose features of the turntable 16 that pertain to the present inventionwill be described. The turntable 16 includes a rotating portion 48 and astationary base portion 50. The rotating portion 48 includes a top 52, afirst activation/deactivation ring 54 (hereinafter “first ring 54”)located between the top 52 and the base portion 50, and a secondactivation/deactivation ring 56 (hereinafter “second ring 56”) locatedbetween the first ring 54 and the base portion 50. The top 52, the firstring 54, and the second ring 56 are mechanically connected together suchthat when the rotating portion 48 rotates about an axis of rotation 58,the top 52, the first ring 54, and the second ring 56 rotate together asa unit relative to the stationary base portion 50. Further, the rotatingportion 48 can rotate in either a clockwise or counterclockwisedirection.

The welding robots 18 are mounted to the top 52 of the rotating portion48 and rotate with and in the same direction as the rotating portion 48.Thus, the rotating portion 48 of the turntable 16 rotates such that thewelding robots 18 can be rotated to any one of the four welding cells12-X. Further, the welding robots 18 are mounted adjacent to each othersuch that during a welding operation both welding robots 18 perform awelding operation in the same welding cell 12-X. It should be noted thatthe welding robots 18 are of the type commonly known in the art, such asbut not limited to MIG welders, and will not be described herein. In theembodiment shown in the figures, there are two welding robots. Thepresent invention, however, is not dependent on the number of weldingrobots. The number of welding robots may vary depending on theapplication. Thus, the embodiment shown in the figures is forillustrative purposes only and is not intended to limit the scope of thepresent invention.

Referring to FIG. 3, although the first ring 54 and the second ring 56both rotate about the axis of rotation 58 they are not concentric. Inother words, the first ring 54 and the second ring 56 are circular inshape but are situated such that a center of the first ring 54 and acenter of the second ring 56 are offset in opposite directions from theaxis or rotation 58. Thus, one side of the first ring 54 extends furtherfrom the axis of rotation 58 of the rotating portion 48 than theopposite side. Similarly, one side of the second ring 56 extends furtherfrom the axis of rotation 58 of the rotating portion 48 than theopposite side. This allows the first ring 54 and the second ring 56 toengage limit switches, which activate and deactivate the light curtains14, upon rotation of the rotating portion 48. Specifically, as therotating portion 48 rotates the first ring 54 engages a first set oflimit switches LS-1, LS-3, LS-5, and LS-7 to thereby activate anddeactivate the perimeter vertical light curtains 14-V and the perimeterhorizontal light curtains 14-H. Further, as the rotating portion 48rotates the second ring 56 engages a second set of limit switches LS-2,LS-4, LS-6, and LS-8 to thereby activate and deactivate the inner lightcurtains 14-I.

Referring to FIGS. 2 and 3, the limit switches are equidistantly spacedaround the turntable 16 such that the limit switches are arranged whereLS-1 and LS-2 correspond to the first welding cell 12-1, LS-3 and LS-4correspond to the second welding cell 12-2, LS-5 and LS-6 correspond tothe third welding cell 12-3, and LS-7 and LS-8 correspond to the fourthwelding cell 12-4. For simplicity, only limit switches LS-1 and LS-2that corresponds to the first welding cell 12-1 will be described.

FIG. 5 illustrates in table form when the light curtains 14-V1, 14-H1,14-I1 are activated and deactivated. When the welding robots 18 arepositioned in the first welding cell 12-1, the first ring 54 engageslimit switch LS-1 and simultaneously disengages limit switches LS-3,LS-5, and LS-7. Accordingly, limit switch LS-1 activates perimetervertical light curtain 14-V1 and perimeter horizontal light curtain14-H1. Thus, the perimeter around the first welding cell 12-1 is guardedby perimeter vertical light curtain 14-V1 and the perimeter horizontallight curtain 14-H1. In addition, limit switches LS-2, LS-3, and LS-4deactivate perimeter vertical light curtains 14-V2, 14-V3, and 14-V4,and the perimeter horizontal light curtains 14-H2, 14-H3, and 14-H4respectively. Thus, personnel can access the welding area 20 and thework areas 22 for the second 12-1, third 12-3, and fourth 12-4 weldingareas. Simultaneously, the second ring 56 disengages limit switch LS-2and engages limit switches LS-4, LS-6, and LS-8. Accordingly, limitswitch LS-2 deactivates inner light curtain 14-I1 and limit switchesLS-4, LS-6, and LS-8 activate inner light curtains 14-I2, 14-I3, and14-I4 respectively. Thus, the welding robots 18 have access to the firstwelding cell 12-1 and the perimeter around the turntable 16 is guardedby inner light curtains 14-I2, 14-I3, and 14-I4.

Referring to FIGS. 2, 3 and 6, the turntable welding system 10 furtherincludes four proximity switches 60-1, 60-2, 60-4, and 60-P (hereinaftercollectively referred to as proximity switches “60”) located adjacent tothe turntable 16. The proximity switches 60 operate on a binary formatto detect the general position of the rotating portion 48 of theturntable 16. Thus, when proximity switch 60-1 is activated indicatesthat the rotating portion 48 of the turntable 16 is at the first weldingcell 12-1. Similarly, when the proximity switch 60-2 is activatedindicates that the rotating portion 48 of the turntable 16 is at thesecond welding cell 12-2. When proximity switches 60-1 and 60-2 areactivated indicates that the rotating portion 48 of the turntable 16 isat the third welding cell 12-3. Finally, when proximity switch 60-4 isactivated indicates that the rotating portion 48 of the turntable 16 isat the fourth welding cell 12-1. Proximity switch 60-P is used forparity. In other words, proximity switch 60-P will turn on when there isonly one other proximity switch turned on and will remain off when twoother proximity switches are turned on. Thus, the number of proximityswitches 60 that will be turned on when the welding robots 18 arepositioned at any given welding cell 12-X will be even (even parity) andmore specifically will be two, as shown in the table in FIG. 6.

Referring to FIG. 1, the turntable welding system 10 further includesmultiple start pushbuttons 62, and a main power pushbutton 64. There aretwo start pushbuttons 62 per welding cell 12-X. The start pushbuttons 62are located at the rear portion of the work area 22 and include anE-stop feature. Each start pushbutton 62 must be activated by apersonnel worker in order for the welding robots 18 to operate in thatgiven welding cell 12-X.

The main power pushbutton 64 controls the power to the entire turntablewelding system 10 and also includes an E-stop feature. In the embodimentshown in the figures the main power pushbutton 64 is located at the rearportion of the work area 22 of welding cell 12-1. The main powerpushbutton 64, however, can be positioned at any location around theperimeter of the turntable welding system 10.

Operation of the turntable welding system 10 will now be described inreference to the first welding process P1, which corresponds to thefirst welding cell 12-1 and the second welding cell 12-2. To effectivelyillustrate the advantage of the present invention the following will beassumed;

-   -   A first welding assembly has already undergone the primary        welding operation P1-P in the first welding cell 12-1 and is        located in the second welding cell 12-2.    -   The first welding assembly is currently undergoing the secondary        welding process P1-S in the second welding cell 12-2.    -   A second welding assembly has also undergone the primary welding        process P1-P in the first welding cell 12-1 and has been removed        from the first welding cell 12-1 and placed in a buffer area 66        (shown in FIG. 1) located between the first welding cell 12-1        and the second welding cell 12-2.    -   A third welding assembly has been loaded into the first welding        cell 12-1 waiting to undergo the primary welding operation P1-P        of the first process P1. It should be noted that the loading of        the third welding assembly into the first welding cell 12-1        occurred during the secondary welding operation P1-S to the        first welding assembly in the second welding cell 12-2.

Thus, at this point in the first welding process P1, when the firstwelding assembly is in the second welding cell 12-2 undergoing thesecondary welding operation P1-S, as explained above, perimeter verticallight curtain 14-V2 and perimeter horizontal light curtain 14-H2 areactivated, and perimeter vertical light curtain 14-V1 and perimeterhorizontal light curtain 14-H1 are deactivated. In addition, inner lightcurtain 14-I2 is deactivated and inner light curtain 14-I1 is activated.

Referring now to the flow chart in FIG. 7, once the secondary weldingoperation P1-S to the first welding assembly is complete, the rotatingportion 48 of the turntable 16 rotates to position the welding robots 18at the first welding cell 12-1 to perform the primary welding operationP1-P to the third welding assembly (STEP 100). Perimeter vertical lightcurtain 14-V1 and perimeter horizontal light curtain 14-H1 at the firstwelding cell 12-1 are activated via limit switch LS-1 and inner lightcurtain 14-I1 is deactivated via limit switch LS-2 (STEP 102). Inaddition, perimeter vertical light curtain 14-V2 and perimeterhorizontal light curtain 14-H2 at the second welding cell 12-2 aredeactivated via limit switch LS-3 and inner light curtain 14-I2 isactivated via limit witch LS-4 (STEP 102). The primary welding operationP1-P to the third welding assembly can now begin.

During the primary welding operation P1-P to the third welding assemblyin the first welding cell 12-1 (STEP 104), the first welding assembly isremoved from the second welding cell 12-2 for further processing (STEP106). In addition, the second welding assembly is then removed from thebuffer area 66 and placed in the fixture in the second welding cell 12-2(STEP 108). Once the primary welding operation P1-P to the third weldingassembly is complete (STEP 110) the rotating portion 48 of the turntable16 rotates to position the welding robots 18 at the second welding cell12-2 to perform the secondary welding operation P1-S to the secondwelding assembly (STEP 112). Again, perimeter vertical light curtain14-V2 and perimeter horizontal light curtain 14-H2 at the second weldingcell 12-2 are activated via limit switch LS-3 and the inner lightcurtain 14-I2 is deactivated via limit switch LS-4 (STEP 114). Inaddition, perimeter vertical light curtain 14-V1 and perimeterhorizontal light curtain 14-H1 at the first welding cell 12-1 aredeactivated via limit switch LS-1 to allow personnel workers to enterthe first welding cell 12-1, and inner light curtain 14-I1 is activatedvia limit switch LS-2 to detect the entry of personnel workers into theturntable area (STEP 114).

During the secondary welding operation P1-S to the second weldingassembly in the second welding cell 12-2 (STEP 116), the third weldingassembly is removed from the first welding cell 12-1 and placed in thebuffer area 66 (STEP 118). A fourth welding assembly is then loaded intothe fixture in the first welding cell 12-1 waiting to undergo theprimary welding operation P1-P (STEP 120). The above process is repeateduntil all the scheduled welding assemblies have undergone the firstwelding process P1 (STEP 122).

Once the first welding process P1 is complete the second welding processP2 will begin to process a different set of welding assemblies in thethird 12-3 and fourth 12-4 welding cells (STEP 124). The second weldingprocess P2 will undergo the process explained above until all thescheduled welding assemblies are complete (STEP 126).

The advantage of the above process is that production of the weldingassemblies is not interrupted each and every time a welding assembly isremoved or loaded into a welding cell 12-X. As illustrated above awelding operation is always in process in a first welding cell while asecond welding cell is being prepared for another welding operation,which increases production and reduces manufacturing costs. Further, thefootprint of the circular arrangement of the welding cells is compact,which makes the manufacturing area efficient for personnel workers toenter the welding cells and retrieve components to perform theirfunctions. Still further, the addition of the light curtains reduces thenumber of physical barriers around the manufacturing area andspecifically around the welding cells, which allows easy unobstructedaccess to the welding cells.

Still yet another advantage to the above process is that duringoperation of the first welding process P1 described above, all theperimeter light curtains (14-V3, 14-V4, 14-H3, 14-H4) located at thethird 12-3 and the fourth 12-4 welding cells are deactivated. Thus,personnel workers can prepare the third 12-3 and fourth 12-4 weldingcells for the second welding process P2 without disrupting the firstwelding process in the first 12-1 and second 12-2 welding cells.Similarly, during operation of the second welding process P2, all theperimeter light curtains (14-V1, 14-V2, 14-H1, 14-H2) located at thefirst 12-1 and the second 12-2 welding cells are deactivated. Thus,personnel workers can prepare the first 12-1 and second 12-2 weldingcells for the first welding process P1 without disrupting the secondwelding process in the third 12-3 and fourth 12-4 welding cells.

Still yet another advantage to the above process is that additional workto a welding assembly located in the buffer area 66 can undergo furtherwork without disrupting the flow of production. For example, additionalhand welding, cleaning or placement of additional parts, etc. can beperformed to the welding assembly while the welding assembly is in thebuffer area 66. It should be noted that an additional buffer area 68(shown only in FIG. 1) is located between the third 12-3 and the fourth12-4 welding cells for use during the second welding process P2.

It should be noted that the terms “first welding process P1” and “secondwelding process P2” are used in the present application to simplify theexplanation of the operation of the turntable welding system and are notintended to limit the scope of the invention. In other words, thewelding process performed in the first 12-1 and second 12-2 weldingcells may be one type of welding process for one type of weldingassembly, and a subsequent welding process preformed in the first 12-1and second 12-2 welding cells may be a different type of welding processfor a different type of welding assembly. Similarly, the welding processperformed in the third 12-3 and fourth 12-4 welding cells may be onetype of welding process for one type of welding assembly, and asubsequent welding process preformed in the third 12-3 and fourth 12-4welding cells may be a different type of welding process for a differenttype of welding assembly.

While specific embodiments of the invention have been described andillustrated, it is to be understood that these embodiments are providedby way of example only and that the invention is not to be construed asbeing limited but only by proper scope of the following claims.

1. A robotic welding system comprising: multiple welding cells includinga first pair of welding cells and a second pair of welding cellsequidistantly spaced in a circular arrangement; a turntable centrallylocated in the circular arrangement, the turntable having a stationaryportion and a rotating portion, the rotating portion including: a topportion; a first ring located between the top portion and the stationaryportion; and a second ring located between the first ring and thestationary portion; multiple welding robots operatively attached to therotating portion of the turntable; multiple perimeter light curtainspositioned at a perimeter of the multiple welding cells; multiple innerlight curtains located between the turntable and a front portion of eachmultiple welding cell; a first set of multiple limit switches; and asecond set of multiple limit switches, wherein the first ring engagesthe first set of multiple limit switches to activate and deactivate theperimeter light curtains, and wherein the second ring engages the secondset of multiple limit switches to activate and deactivate the innerlight curtains.
 2. The robotic welding system of claim 1, wherein duringa first time period the welding robots rotate between the first pair ofwelding cells to perform a first welding process, wherein during asecond time period the welding robots rotate between the second pair ofwelding cells to perform a second welding process, and wherein the firstwelding process may be substantially different from the second weldingprocess.
 3. The robotic welding system of claim 2, wherein the firstpair of welding cells includes a primary welding cell and a secondarywelding cell, wherein the first welding process includes a primarywelding operation performed in the primary welding cell and a secondarywelding operation performed in the secondary welding cell, and whereinthe primary welding operation is substantially different from thesecondary welding operation.
 4. The robotic welding system of claim 3,wherein the second pair of welding cells includes a primary welding celland a secondary welding cell, and wherein the second welding processincludes a primary welding operation performed in the primary weldingcell and a secondary welding operation performed in the secondarywelding cell, and wherein the primary welding operation is substantiallydifferent from the secondary welding operation.
 5. The robotic weldingsystem of claim 4, wherein during the primary welding operation in theprimary welding cell the perimeter light curtains for the primarywelding cell are activated and the perimeter light curtains for thesecondary welding cell are deactivated to allow preparation of thesecondary welding cell for the secondary welding operation, and whereinduring the secondary welding operation in the secondary welding cell theperimeter light curtains for the secondary welding cell are activatedand the perimeter light curtains for primary welding cell aredeactivated to allow preparation of the primary welding cell for theprimary welding operation.
 6. The robotic welding system of claim 5,wherein during the primary welding operation in the primary welding cellthe inner light curtain for the primary welding cell is deactivated andthe remaining inner light curtains are activated, and wherein during thesecondary welding operation in the secondary welding cell the innerlight curtain for the secondary welding cell is deactivated and theremaining inner light curtains are activated.
 7. The robotic weldingsystem of claim 6, wherein each perimeter light curtain includes avertical light curtain and a horizontal light curtain, wherein thevertical light curtain includes a mirror, and wherein the mirrordeflects a light beam at a predetermined angle from a transmitter postof the vertical light curtain to a receiver post of the vertical lightcurtain.
 8. The robotic welding system of claim 7 further comprisingproximity switches to detect the position of the rotating portion of theturntable.
 9. A robotic welding system comprising: a first welding cellto perform a primary welding operation; a second welding cell to performa secondary welding operation; a turntable having a stationary portionand a rotating portion, the rotating portion including: a top portion; afirst ring located between the top portion and the stationary portion;and a second ring located between the first ring and the stationaryportion; a welding robot operatively attached to the rotating portion;multiple perimeter light curtains positioned at a perimeter of the firstwelding cell and the second welding cell; an inner light curtain locatedbetween the turntable and a front portion of both the first welding celland the second welding cell; a first set of multiple limit switches; anda second set of multiple limit switches, wherein the first ring engagesthe first set of multiple limit switches to activate and deactivate theperimeter light curtains, and wherein the second ring engages the secondset of multiple limit switches to activate and deactivate the innerlight curtain.
 10. The robotic welding system of claim 9, wherein theturntable is located adjacent to the first and second welding cells suchthat the welding robot can perform the primary and secondary weldingoperations in the first and second welding cells respectively, whereinduring the primary welding operation in the first welding cell theperimeter light curtains for the first welding cell are activated andthe perimeter light curtains for the second welding cell are deactivatedto allow the preparation of the second welding cell for the secondarywelding operation, wherein during the secondary welding operation in thesecond welding cell the perimeter light curtains for the second weldingcell are activated and the perimeter light curtains for the firstwelding cell are deactivated to allow the preparation of the firstwelding cell for the primary welding operation, and wherein the primarywelding operation is substantially different from the secondary weldingoperation.
 11. The robotic welding system of claim 10, wherein duringthe primary welding operation in the first welding cell the perimeterlight curtains for the first welding cell are activated and theperimeter light curtains for the second welding cell are deactivated toallow preparation of the second welding cell for the secondary weldingoperation, and wherein during the secondary welding operation in thesecond welding cell the perimeter light curtains for the second weldingcell are activated and the perimeter light curtains for first weldingcell are deactivated to allow preparation of the first welding cell forthe primary welding operation.
 12. The robotic welding system of claim11, wherein during the primary welding operation in the first weldingcell the inner light curtain for the first welding cell is deactivatedand the inner light curtain for the second welding cell is activated,and wherein during the secondary welding operation in the second weldingcell the inner light curtain for the second welding cell is deactivatedand the inner light curtain for the first welding cell is activated. 13.The robotic welding system of claim 12, wherein each perimeter lightcurtain includes a vertical light curtain and a horizontal lightcurtain, wherein the vertical light curtain includes a mirror, andwherein the mirror deflects a light beam at a predetermined angle from atransmitter post of the vertical light curtain to a receiver post of thevertical light curtain.
 14. The robotic welding system of claim 13further comprising proximity switches positioned adjacent to theturntable to detect the position of the rotating portion of theturntable.